Cleaning up / restoring threads in a radiator for a steam valve

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Old 12-01-12, 06:35 AM
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Cleaning up / restoring threads in a radiator for a steam valve

Have a radiator with a steamy leak at the steam valve that I'd like to clean up.

The threads on the radiator were stripped long before I came along. Using goop and teflon tape and the threads of a tapered valve have plugged it but... would like to just fix it so I don't have thoughts of it blowing off.

How does one rethread the hole if the hole has become too wide to accept a valve securely; what size tap, type of adapter or what to use?
 
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Old 12-01-12, 07:08 AM
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The steam valve

If it't a silver thing on one end of your radiator, it's actually an air valve that vents air from the rad, as the steam comes up to heat the room. It has a 1/8 th pipe thread nipple that threads into the rad. The 1/8 th pipe tap is usually available in any good hardware store of a box store. When you buy one, get the "T" handle also, as it will be much easier to work it. Since you said the old valve was kind of beat up, you might as well get a new one, and while your at it, and maybe a spare, so you can switch valves,if you find another that dosen't work. When cleaning up the beat up threaded hole, just thread enough so that the new valve will go in about 3/4 ths of the way. Don't make the hole too big, or the valve won't get tight.
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Old 12-01-12, 08:10 AM
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If it is pretty loose......you may have to go up one size to stop the leak.

The drill size for 1/8 NPT (National Pipe Thread) is a Letter "Q" drill or 0.332" dia.

You could get away with a 21/64" drill if you don't have Letter drills.

Put that size drill bit in the hole.....if it is really sloppy.....then onward and upward.

You will need a 1/4 NPT tap and a 7/16" (0.438) drill bit.

You will also need a 1/8" to 1/4" brass threaded bushing to bring it back to original size.

Drill out the hole and then start "tapping".....making sure you keep it straight and square.

As stated.....don't go too deep.....this is a tapered thread.

Going too deep will increase the hole size and you'll be faced with the same dilemma.

Back out the tap after 5 or 6 threads.....try the bushing for fit.

Should go in a little more than half way finger tight.....if not tap it a little more.

Put some pipe dope or teflon tape on the threads of the bushing and the new valve.



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Old 12-01-12, 08:30 AM
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Also....as stated.....best to use a proper tap T-handle.

Taps are very hard and brittle.....and can break if you're not careful.

If you snap it off in the hole you'll have a bigger nightmare.

Slow and steady......1/2 turn at a time....back it out a little to clear chips....repeat.



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Old 12-01-12, 09:09 AM
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Thanks. That's what I expected to hear. But not exactly sure on which type of bushing to use. Is it this:

GRAINGER APPROVED VENDOR Pipe Bushing, Brass, 1/4 x 1/8 In, PK10 - Brass Pipe Fittings - 6AYW5|6AYW5 - Grainger Industrial Supply

I have the letter drills and everything else needed, even the lubricant, but the tapered threads threw me for a loop. I'm use to only working with screw threads.

It's beyond simply rethreading the hole, a bushing is required. The valve is stuck in there almost like a cork, I don't know how it's made it so long without blowing off.
 
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